'\" te
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.TH _LWP_MUTEX_LOCK 2 "Jul 30, 1992"
.SH NAME
_lwp_mutex_lock, _lwp_mutex_unlock, _lwp_mutex_trylock \- mutual exclusion
.SH SYNOPSIS
.LP
.nf
#include <sys/lwp.h>

\fBint\fR \fB_lwp_mutex_lock\fR(\fBlwp_mutex_t *\fR\fImp\fR);
.fi

.LP
.nf
\fBint\fR \fB_lwp_mutex_trylock\fR(\fBlwp_mutex_t *\fR\fImp\fR);
.fi

.LP
.nf
\fBint\fR \fB_lwp_mutex_unlock\fR(\fBlwp_mutex_t *\fR\fImp\fR);
.fi

.SH DESCRIPTION
.sp
.LP
These functions serialize the execution of lightweight processes. They are
useful for ensuring that only one lightweight process can execute a critical
section of code at any one time (mutual exclusion). LWP mutexes must be
initialized to 0 before use.
.sp
.LP
The \fB_lwp_mutex_lock()\fR function locks the LWP mutex pointed to by
\fImp\fR. If the mutex is already locked, the calling LWP blocks until the
mutex becomes available. When \fB_lwp_mutex_lock()\fR returns, the mutex is
locked and the calling LWP is the "owner".
.sp
.LP
The \fB_lwp_mutex_trylock()\fR function attempts to lock the mutex. If the
mutex is already locked it returns with an error. If the mutex is unlocked, it
is locked and \fB_lwp_mutex_trylock()\fR returns.
.sp
.LP
The \fB_lwp_mutex_unlock()\fR function unlocks a locked mutex. The mutex must
be locked and the calling LWP must be the one that last locked the mutex (the
owner). If any other LWPs are waiting for the mutex to become available, one of
them is unblocked.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, \fB0\fR is returned. A non-zero value indicates an
error.
.SH ERRORS
.sp
.LP
If any of the following conditions are detected, \fB_lwp_mutex_lock()\fR,
\fB_lwp_mutex_trylock()\fR, and \fB_lwp_mutex_unlock()\fR fail and return the
corresponding value:
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The \fImp\fR argument points to an invalid LWP mutex.
.RE

.sp
.ne 2
.na
\fB\fBEFAULT\fR\fR
.ad
.RS 10n
The \fImp\fR argument points to an illegal address.
.RE

.sp
.LP
If any of the following conditions occur, \fB_lwp_mutex_trylock()\fR fails and
returns the corresponding value:
.sp
.ne 2
.na
\fB\fBEBUSY\fR\fR
.ad
.RS 9n
The \fImp\fR argument points to a locked mutex.
.RE

.SH SEE ALSO
.sp
.LP
.BR Intro (2),
.BR _lwp_cond_wait (2)
